Chloride (Cl-) is the major extracellular anion in the body, accompanying sodium (Na+), and is primarily derived from dietary sources. Data suggest that increased dietary Cl- intake increases blood pressure, yet paradoxically, higher serum Cl- appears associated with lower mortality and cardiovascular risk. This implies that serum Cl- also reflects risk pathways independent of blood pressure, serum Na+, and bicarbonate (HCO3-). We analyzed 12,968 hypertensive individuals followed up for 35 years, using Cox proportional hazards model to test whether baseline serum Cl- was an independent predictor of mortality. To distinguish the effect of Cl- from Na+ and HCO3-, we adjusted for these electrolytes and also performed the analysis stratified by Na+ /HCO3- and Cl- levels. Generalized estimating equation was used to determine the effect of baseline Cl- on follow-up blood pressure. The total time at risk was 19,7101 person-years. The lowest quintile of serum Cl- (<100 mEq/L) was associated with a 20% higher mortality (all-cause, cardiovascular and noncardiovascular) compared with the remainder of the subjects. A 1 mEq/L increase in serum Cl- was associated with a 1.5% (hazard ratio, 0.985; 95% confidence interval, 0.98-0.99) reduction in all-cause mortality, after adjustment for baseline confounding variables and Na+, K+ , and HCO3- levels. The group with Na+ > 135 and Cl- > 100 had the best survival, and compared with this group, the Na+ >135 and Cl- <100 group had significantly higher mortality (hazard ratio, 1.21; 95% confidence interval, 1.11-1.31). Low, not high Serum Cl- (<100 mEq/L), is associated with greater mortality risk independent of obvious confounders. Further studies are needed to elucidate the relation between Cl- and risk.
Keywords: chlorides; epidemiology; hypertension; mortality; sodium.